This invention pertains to the dimerization of methacrylic acid derivatives and more particularly to the dimerization of methacrylic acid and methacrylic acid derivatives in the presence of an organic Co(II) catalyst to produce 2,2-dimethyl-4-methyleneglutaric acid derivatives.
The importance of difunctional materials in the synthesis of useful polymeric materials is well known. Diols and diacids are used in the production of polyesters. Difunctional isocyanates are used for the production of polyurethanes and for the crosslinking of polyfunctional resins. Diepoxides are widely used for a variety of coating materials or as crosslinkers for acid functional materials. One method of preparing a new class of difunctional materials is through the dimerization of monofunctional methacrylic acid derivatives carrying the desired functionality.
The 2,2-dimethyl-4-methyleneglutaric acid derivatives have been synthesized previously in low yield as side reactions. For instance, carbonylation of allene in water in the presence of ruthenium catalysts produced methacrylic acid as well as some methyleneglutarate derivative (J. Org. Chem., 26, 3126, 1961). Similarly, base catalyzed (sodium alkoxide) oligomerization of vinyl monomers produced low yields of alpha-methylene glutaric acid derivatives according to European Polymer Journal, Vol. 7, pages 1435-1443 (1971). Thermal initiated methyl methacrylate oligomer apparently produces minor yields of cyclic dimers and linear trimers thereof as suggested in European Polymer Journal, Vol. 16, pages 785-791 (1980). All of the disclosed methods, however, produce very low yields and are unacceptable for commercial processes. A recent publication has suggested the use of cobalt porphyrin complex as a catalyst for chain transfer to monomer generally for producing oligomers and polymers, as disclosed in J. Poly. Chem., Ed., Vol. 19, 877 (1981).
It now has been found that 2,2-dimethyl-4-methyleneglutaric acid and derivatives thereof can be synthezied by dimerization of a methacrylic monomer in the presence of an organic Cobalt(II) catalyst in a free radical process to produce a predominately dimerized product comprising 2,2-dimethyl-4-methyleneglutaric acid (2,2,4-DMMG) and derivatives thereof. The process provides an excellent improvement over prior art methods of controlling the dimerization of methacrylic monomers. In accordance with this invention, the Co(II) catalyst effectively functions as a catalyst to effect a free radical dimerization of methacrylic monomers to produce the dimer. The resulting DMMG derivative can be used as a diacid for reaction with glycols to produce polyesters exhibiting good hydrolysis resistance and the ability to produce air-dry tack-free surface. Polymers produced from the DMMG derivatives are generally useful as binders in protective coatings. Glutaric acid derivative dimers produced in accordance with the process of this invention resulted in yields of between 60% and 80% or more based on the methacrylate monomer conversion to dimer. These and other advantages of this invention will become more apparent by referring to the detailed description of the invention and the illustrative examples.